Gn. Andrianov et al., ELECTROPHYSIOLOGICAL DEMONSTRATION OF N-METHYL-D-ASPARTATE RECEPTORS AT THE AFFERENT SYNAPSE OF CATFISH ELECTRORECEPTOR ORGANS, Neuroscience, 79(4), 1997, pp. 1231-1237
An excitatory amino acid, most probably L-glutamate, acts as a neurotr
ansmitter at the receptor cell-afferent fibre synapses in the ampullar
y electroreceptor organs of the freshwater catfish Ictalurus nebulosus
. In the present study, we have used an electrophysiological approach
to investigate the presence of N-methyl-D-aspartate receptors at this
level. N-Methyl-D-aspartate, dissolved in an Mg2+-containing (normal)
solution, had no effect on afferent activity, not even at 5 mM. Howeve
r, addition of 5 mM N-methyl-D-aspartate to an Mg2+-free solution evok
ed an enduring increase in firing rate. The application of N-methyl-D-
aspartate combined with electrical sine wave stimulation produced a fi
ring increase in the primary afferents, even in the presence of Mg2+ (
1.5 mM). Glycine (0.01-0.001 mM) significantly potentiated the N-methy
l-D-aspartate responses. Addition of antagonists of the actions of N-m
ethyl-D-aspartate, 7-chlorokynurenic acid, DL-2-amino-5-phosphonovaler
ic acid and ketamine in concentrations of 0.5-2.0 mM led to a decrease
in resting and stimulus-evoked activity. 7-Chlorokynurenic acid also
blocked the responses to application of N-methyl-D-aspartate. The glyc
ine agonist D-serine (0.01 mM) prevented the 7-chlorokynurenic inhibit
ory effect. These results suggest the involvement of N-methyl-D-aspart
ate receptors in mediating the actions of L-glutamate at the afferent
synapses of the electroreceptor organs of the catfish. Copyright (C) 1
997 Published by Elsevier Science Ltd.